Performance between SQL Statement and Dynamic SQL

Question

Select emp_id
into id_val
from emp
where emp_id = 100
EXECUTE IMMEDIATE
'Select '|| t_emp_id ||
'from emp '
'where emp_id = 100'
into id_valWill there be more impact in performance while using Dynamic SQL?

Answer 1

CP wrote:
Will there be more impact in performance while using Dynamic SQL?All SQLs are parsed and executed as SQL cursors.
The 2 SQLs (dynamic and static) results in the exact same SQL cursor. So both methods will use an identical cursor. There are therefore no performance differences ito of how fast that SQL cursor will be.
If an identical SQL cursor is not found (a soft parse), the SQL engine needs to compile the SQL source code supplied, into a SQL cursor (a hard parse).
Hard parsing burns a lot of CPU cycles. Soft parsing burns less CPU cycles and is therefore better. However, no parsing at all is the best.
To explain: if the code creates a cursor (e.g. INSERT INTO tab VALUES( :1, :2, :3 ) for inserting data), it can do it as follows:
while More Data Found loop
  parse INSERT cursor
  bind variables to INSERT cursor
  execute INSERT cursor
  close INSERT cursor
end loopIf that INSERT cursor does not yet exists, it will be hard parsed and a cursor created. Each subsequent loop iteration will result in a soft parse.
However, the code will be far more optimal as follows:
parse INSERT cursor
while More Data Found loop
  bind variables to INSERT cursor
  execute INSERT cursor
end loop
close INSERT cursorWith this approach the cursor is parsed (hard or soft), once only. The cursor handle is then used again and again. And when the application is done inserting data, the cursor handle is released.
With dynamic SQL in PL/SQL, you cannot really follow the optimal approach - unless you use DBMS_SQL (a complex cursor interface). With static SQL, the PL/SQL's optimiser can kick in and it can optimise its access to the cursors your code create and minimise parsing all together.
This is however not the only consideration when using dynamic SQL. Dynamic SQL makes coding a lot more complex. The SQL code can now only be checked at execution time and not at development time. There is the issue of creating shareable SQL cursors using bind variables. There is the risk of SQL injection. Etc.
So dynamic SQL is seldom a good idea. And IMO, the vast majority of people that post problems here relating to dynamic SQL, are using dynamic SQL unnecessary. For no justified and logical reasons. Creating unstable code, insecure code and non-performing code.